It is frequently necessary to provide environmental protection around a cable splice to keep contaminants such as water away from the spliced conductors. In the case of telecommunications cables and other multiconductor cables a large splice bundle will be produced, joining the two cables and some mechanical protection around it is often required. Thus, the enclosure (referred to as a splice case) may comprise a liner, which is shaped to encompass the bulky splice bundle and to taper down to the cables at either end, and an impervious outer layer. In recent years this impervious outer layer has been provided by a dimensionally-recoverable, generally heat-shrinkable, sleeve. Such a sleeve is installed around the splice and liner and then shrunk down to engage the liner and the spliced cables. The sleeve may be tubular (i.e. closed in cross-section) in which case it is slid along one of the cables until it overlies the splice, or it may be of the wrap-around type, in which case it is wrapped directly around the splice and secured in the wrapped around configuration. An advantage of dimensional recovery is that the sleeve can be supplied oversized in order that it be an easy fit, and in order that close manufacturing tolerances be avoided. When approximately in position it is caused dimensionally to recover (generally to shrink radially) to engage the cables either side of the splice and optionally also the splice and liner, thereby forming an environmental seal. Recovery is conveniently brought about by heating, and the sleeve may be internally coated with a heat-activatable sealing material, which will be activated by the same heating step that was carried out to induce recovery. Such recoverable sleeves are well known in the telecommunications cable accessories art, and are marketed under the Raychem Trade Marks XAGA and VASM. Wrap-around sleeves are disclosed in GB 1155470 (Raychem).
Traditionally, heat-recoverable sleeves have been heated by use of an open-flame torch although electrical heating has been proposed for use in dangerous environments. Examples of electrically heatable sleeves are given in EP 0158519 (Raychem) and EP0117762 (Raychem).
Problems with wrap-around, recoverable sleeves may arise where a larger transition has to be covered ("transition" refers to a difference in diameter for example between cables and splice bundle) or where branching cables have to be sealed. In each of these cases it may be necessary to employ much adhesive in order to provide a reliable seal; and much adhesive may be difficult to activate since the quantity of heat required may be large, and the adhesive may be shielded from an external heat source. In the first of these cases a difficulty may arise because a sleeve of high recovery may need to be used in order that it surround the bulky splice before shrinkage and engage the small cables after shrinkage. Such a sleeve may be difficult to produce especially if it is to comprise a conductive polymer having the desired self-heating properties. An alternative solution may be to build-up the cable to a suitable diameter with adhesive, but then problems of adhesive activation may become worse. In the second case difficulty arises because two side-by-side, branching, cables present a rentrant or concave cross-section to the surrounding sleeve. Tent-shaped voids will thus remain between the shrunk sleeve and the underlying pair of cables, through which contaminants can enter the splice case. Such voids may be filled with adhesive, but that again may give rise to the problem of activating a mass of adhesive that is shielded from any external heat source. An excellent branching technique is disclosed in GB 1604981 (Raychem), and in EP 0151512 (Raychem). The latter relates to electrical heating using a specially designed and perhaps rather expensive clip.
A solution to the problem of the need for a high recovery ratio in an electrically-heatable sleeve that cannot be highly expanded is given in EP 0117762 (Raychem). There is a sleeve shown which when in the wrapped configuration is of, say, frusto-conical shape. In the unwrapped configuration, the sleeve therefore has closure members which are non-parallel. Thus a large difference between the unrecovered dimension of one end and the recovered dimension of an opposite end results from the combination of a moderate recovery ratio and an initial difference in size. That solution is not, however, ideal since any given sleeve cannot be used over a wide range of cable sizes and shapes, and such sleeves are difficult to manufacture having tapers at both ends.